Method and apparatus for removing additives from thermoplastic resin composition

ABSTRACT

There is provided a treatment method of efficiently separating an additive component from a resin component for the purpose of treating and recycling a thermoplastic resin composition containing an additive. The treatment method includes heating and agitating the thermoplastic resin composition containing the additive together with a solvent for dissolving at least part of the additive at a temperature ranging from the glass transition temperature of the thermoplastic resin to the boiling point of the solvent inclusive, and separating and recovering the solvent in a liquid state in which at least part of the additive is dissolved, so that at least part of the additive is separated and removed from the thermoplastic resin composition.

This application is a divisional of U.S. patent application Ser. No.10/469,712, filed Mar. 18, 2004, which is a U.S. National PhaseApplication of PCT International Application PCT/JP2002/01768, filedFeb. 27, 2002, the entire disclosure of which is incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a treatment method and a treatmentapparatus of separating and removing additive components from athermoplastic resin composition containing various additives. Forexample, the present invention is useful for separating and removingadditive components from housings made of resins containing the additivecomponents for home electric appliances to be recovered according to theElectric Appliance Recycling Law. In particular, it is effective forseparating and removing flame retardants and flame retardant auxiliariesfrom the thermoplastic resin composition containing the flameretardants, flame retardant auxiliaries and the like to be used ashousings for TVs and PC monitors.

BACKGROUND ART

At present, thermoplastic resins such as propylene resins, styreneresins, acrylonitrile/butadiene/styrene (ABS) resins, and high-impactpolystyrene resins having improved impact resistance are generally usedfor housings of TVs and PC monitors and those for various home electricappliances. These are used with additive components incorporated for thepurpose of imparting various functions to the resins. For example, asthermoplastic resins have high combustibility by themselves, the resinsare mixed with flame retardants and flame retardant auxiliaries in aproportion of about 10 to 25% by weight from the viewpoint of preventingthe spread of fire during the fire. In particular, bromine-based flameretardants have a high flame retarding effect on various resins and havea low price, so that they have been globally used.

The bromine-based flame retardants have excellent flame retardancy toaromatic resins represented by styrenic resins and have been used inlarge quantities for various housings and component materials in homeelectric appliances. Hence, resin compositions containing thebromine-based flame retardants are discarded in large quantities whenthese home electric appliances are scrapped.

Generally, in the methods of treating resin wastes, incineration andlandfill have been mainly employed and only a part of them is recycledthrough heating/melting or the like. It is desired to dispose of wasteplastics by incineration considering shortages of landfill site.However, the resin compositions containing flame retardancy finddifficulty in incineration due to the high degree of flame retardancyimparted thereto, finding difficulty in disposing.

In addition, as awareness to environmental issues is raised, the harmfuleffect of halogenated organic substances on environment is pointed outand the use of the halogenated organic substances is being restricted.At present, each of the users is under review of switching thehalogenated flame retardants to the flame retardants containing nohalogenated organic substances such as phosphorus-based compounds.However, the phosphorus-based compounds have less capability ofimparting flame retardancy compared to the halogenated organicsubstances, so that the present situation is that the switching from thehalogenated organic substances almost stops.

Further, in recent years, the reuse of the resources derived frompetroleum chemistry is strongly requested and the establishment of themethods of resin waste disposal and recycling has become an importantissue. Particularly, the Electric Appliance Recycling Law that has comeinto effect since April 2001 requests suitable recycling treatment on TVsets, refrigerators, air conditioners, and washing machines.

For the time being the target of the recycling rate is about 50 to 60%,which may be met by the efforts for promoting the recycling of glass andmetal that occupy relatively large proportion by weight in each of theproducts. However, as the target is anticipated to become higher infuture, the establishment of the resin recycling method is desired.

Various studies have been carried out on a method of treating a resincomposition containing a flame retardant. However, these studies mainlyinclude acid treatment (Japanese Patent Laid-Open No. 6-157812) or hightemperature treatment (Japanese Patent Laid-Open No. 8-299759, JapanesePatent Laid-Open No. 9-262565, and Japanese Patent Laid-Open No.2000-198874). They mainly include the thermal cycle treatment in which aresin and a flame retardant are completely decomposed. Almost no effortswith the objective of material recycling of resins are found. JapanesePatent Laid-Open No. 10-195234 proposes a method of separating a flameretardant from a resin by modifying the resin. This method considers theuse of the resin to other applications by functionalizing it. However,we think that the establishment of a recycling method mainly ofrecycling the resin to general-purpose applications is urgent.

DISCLOSURE OF INVENTION

The present invention has been proposed in view of these situations, andit is an object of the present invention to provide a treatment methodand a treatment apparatus in which material recycling is easily possibleon housings made of thermoplastic resins containing additives such as aflame retardant.

The inventors have found a method of separating and removing an additivecomponent such as a flame retardant from a resin by bringing athermoplastic resin composition containing an additive such as a flameretardant into contact under heating with a specific solvent topositively dissolve only the additive component such as the flameretardant from the resin, and have completed the present invention,after having diligently investigated the above described problems.

A first aspect of the present invention is a method of treating athermoplastic resin composition containing an additive, characterized bycomprising: heating and agitating the thermoplastic resin compositioncontaining the additive together with a solvent wherein a solubilityparameter (SP_(solvent)) is not smaller than a solubility parameter ofsaid thermoplastic resin component+1(SP_(resin)+1)((MPa)^(0.5) as theunit), comprising at least one selected from glycol-based solvents,glycol ether-based solvents, lactate-based solvents, or alcohol-basedsolvents having five or more carbon atoms at a temperature ranging froma glass transition temperature of said thermoplastic resin to a boilingpoint of said solvent inclusive; and separating and recovering saidsolvent in a liquid state in which at least part of said additive isdissolved, so that at least part of said additive is separated andremoved from said thermoplastic resin composition.

A second aspect of the present invention is the method of treating athermoplastic resin composition containing an additive according to thefirst aspect of the present invention, characterized in that saidthermoplastic resin composition is a styrenic resin.

A third aspect of the present invention is the method of treating athermoplastic resin composition containing an additive according to thefirst aspect of the present invention, characterized in that saidstyrenic resin comprises any one of poly-styrene, poly-α-methyl styrene,poly-styrene-butadiene, poly-styrene-acrylonitrile,poly-styrene-butadiene-acrylonitrile, poly-styrene-maleic anhydride, andimpact-resistant high-impact polystyrene.

A fourth aspect of the present invention is the method of treating athermoplastic resin composition containing an additive according to thefirst aspect of the present invention, wherein said additive consists oftwo or more additive components and at least part of each of said two ormore additive components is separated and removed from saidthermoplastic resin composition with the solvent for dissolving at leastpart of each of the additive components.

A fifth aspect of the present invention is the method of treating athermoplastic resin composition containing an additive according to thefirst aspect of the present invention, wherein the additive contained insaid thermoplastic resin composition comprises a bromine-based flameretardant and an antimony-based flame retardant auxiliary, and thesolvent wherein a solubility parameter (SP_(solvent)) is not smallerthan a solubility parameter of said thermoplastic resincomponent+1(SP_(resin)+1)((MPa)^(0.5) as the unit), consisting of atleast one selected from glycol-based solvents, glycol ether-basedsolvents, lactate-based solvents, or alcohol-based solvents having fiveor more carbon atoms is used as the solvent for dissolving at least partof the bromine-based flame retardant and the solvent selected fromethylene glycol or propylene glycol is used as the solvent fordissolving at least part of the antimony-based flame retardantauxiliary, so that at least part of each of the bromine-based flameretardant and the antimony-based flame retardant auxiliary is separatedand removed from said thermoplastic resin composition.

A sixth aspect of the present invention is the method of treating athermoplastic resin composition containing an additive according to thefirst aspect of the present invention, wherein the additive contained insaid thermoplastic resin composition comprises a bromine-based flameretardant and an antimony-based flame retardant auxiliary, and thesolvent wherein a solubility parameter (SP_(solvent)) is not smallerthan a solubility parameter of said thermoplastic resincomponent+1(SP_(resin)+1)((MPa)^(0.5) as the unit), consisting of atleast one selected from glycol-based solvents, glycol ether-basedsolvents, lactate-based solvents, or alcohol-based solvents having fiveor more carbon atoms is used as the solvent for dissolving at least partof the bromine-based flame retardant to separate and remove at leastpart of the bromine-based flame retardant from said thermoplastic resincomponent, and then the solvent selected from ethylene glycol orpropylene glycol is used as the solvent for dissolving at least part ofthe antimony-based flame retardant auxiliary to separate and remove atleast part of the antimony-based flame retardant from said thermoplasticresin component.

A seventh aspect of the present invention is an apparatus of treating athermoplastic resin composition containing an additive, comprising:means of charging a solvent wherein a solubility parameter(SP_(solvent)) is not smaller than a solubility parameter of saidthermoplastic resin component+1(SP_(resin)+1)((MPa)^(0.5) as the unit),for dissolving at least part of the additive comprising at least oneselected from glycol-based solvents, glycol ether-based solvents,lactate-based solvents, or alcohol-based solvents having five or morecarbon atoms and the thermoplastic resin composition containing saidadditive; means of heating to a temperature ranging from the glasstransition temperature of said thermoplastic resin to the boiling pointof said solvent inclusive; means of agitating said thermoplastic resincomposition containing the additive and/or said solvent; and means ofseparating the solvent in a liquid state in which at least part of saidadditive is dissolved to the outside of the treatment apparatus.

An eighth aspect of the present invention is an apparatus of treating athermoplastic resin composition containing an additive, comprising: acylinder holding a heating mechanism; a single or a plurality of screwsconnected with a center axis in the cylinder; a drive mechanism at thebase end of the screw axis to rotate the screw; an inlet for athermoplastic resin composition containing said additive and an inletfor a solvent for dissolving at least part of said additive in theneighborhood of the base end of the screw axis, wherein the screw axisis arranged such that the rotation thereof transfers the thermoplasticresin composition containing said additive and said solvent from thebase end side toward the leading end side while pressuring, heating andkneading them; an outlet for discharging said solvent in a liquid statein which at least part of said additive is dissolved, at the locationcloser to the leading end side than said inlet; and an resin extrusionsection for extruding said kneaded and molten thermoplastic resincomposition from which at least part of said additive is separated andremoved, at the leading end.

A ninth aspect of the present invention is an apparatus of treating athermoplastic resin composition containing an additive according to theeighth aspect of the present invention, comprising at least 2 pairs ofthe inlet for the solvent for dissolving at least part of said additiveand the outlet for discharging the solvent in a liquid state in which atleast part of said additive is dissolved, disposed repeatedly in thisorder from the base end toward the leading end.

A tenth aspect of the present invention is an apparatus of treating athermoplastic resin composition containing an additive according to theeighth or the ninth aspect of the present invention, wherein the outletfor discharging the solvent in a liquid state in which at least part ofsaid additive is dissolved is disposed at a lower side than said screwaxis.

An eleventh aspect of the present invention is an apparatus of treatinga thermoplastic resin composition containing an additive according toany of the eighth to the tenth aspects of the present invention, whereina deaeration port for deaerating part of said solvent from said resincomposition is provided between the outlet for discharging the solventin a liquid state in which at least part of said additive and the resinoutlet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an apparatus illustrating the presentinvention;

FIG. 2 is a schematic view of an apparatus illustrating the presentinvention;

FIG. 3 is a schematic view of an apparatus illustrating Example 1 of thepresent invention;

FIG. 4 is a schematic view of an apparatus illustrating Example 2 of thepresent invention;

FIG. 5 is a schematic view of an apparatus illustrating Example 3 of thepresent invention; and

FIG. 6 is a schematic view of an apparatus illustrating Example 4 of thepresent invention.

DESCRIPTION OF SYMBOLS

-   1, 1′: solvent and resin inlet-   2: solvent outlet-   3: heater-   4: reaction vessel-   5: agitator-   6: resin-   7: solvent-   11: kneader-   12: resin inlet (hopper)-   13: screw-   14: heater-   15: cylinder-   16: motor-   17: solvent inlet-   18: solvent outlet-   19: resin outlet (die)-   20: vent-   21: vacuum pump-   22: solvent trap-   23: cooling water bath-   24: cutter-   25: resin pellet-   27: solvent inlet-   28: solvent outlet

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention relates to a treatment method and a treatmentapparatus of bringing a thermoplastic resin composition containing anadditive into contact under heating with a specific solvent andsubjecting them to kneading under heating to obtain a resin from whichat least part of the additive is removed by a simple method.

The thermoplastic resin composition as herein described refers to areject and a fragment formed in a molding process in a manufacturingfield and the like, or a housing resin recovered at recycling locationsas waste home electric appliances. In addition, the additives includematerials that are preferably removed for reuse and recycle such as aflame retardant and a flame retardant auxiliary, as well as astabilizer, a colorant, a plasticizer, a flowability modifier, a releaseagent, and an antioxidant. The resin composition may have a surface onwhich an acrylic coating is applied.

The flame retardants that are known include phenyl ether-based flameretardants such as decabromodiphenyl ether, octabromodiphenyl ether,tetrabromodiphenyl ether; bisphenol A-type flame retardants such astetrabromobisphenol A (TBA); bromine-based flame retardants such ashexabromocyclododecane, bis(tribromophenoxy)ethane, tribromophenol,ethylene bis-tetrabromophthalimide, a TBA polycarbonate oligomer, abrominated polystyrene, a TBA epoxy oligomer; chlorine-based flameretardants such as a chlorinated paraffin, perchloro cyclopentadecane,chlorendic acid; phosphorus-based flame retardants; flame retardantscontaining nitrogen compounds; and inorganic flame retardants.

The flame retardants may be contained singly or in combination in thethermoplastic resin composition. The flame retardants may be a mixtureconsisting of a flame retardant comprising a halogenated organiccompound such as a bromine-based flame retardant and an inorganic flameretardant auxiliary typified by antimony trioxide or the like, dependingon the grade of flame retardancy. The content of the flame retardants isnot limited, but they are typically mixed in approximately 10 to 20% byweight relative to the weight of the resin composition.

On the other hand, the present invention can be applied to anythermoplastic resins such as ethylene resins, propylene resins andstyrenic resins, and is particularly effective for styrenic resins. Thestyrenic resins include resins comprising polystyrene, poly-α-methylstyrene, styrene-butadiene, styrene-acrylonitrile,styrene-butadiene-acrylonitrile, styrene-maleic anhydride, andimpact-resistant high-impact polystyrene.

The above described styrenic resins may be used singly or incombination. They may be a mixture with other resins. The molecularweight of the styrenic resins is not limited, but is preferably fromapproximately 3,000 to 3,000,000 as a weight average molecular weight.

It is generally said that while a group of compounds called a “non-deca”type exhibits generally good solubility to general purpose solvents,decabromodiphenyl ether (popularly called “decabro”) is insoluble in asolvent, among bromine-based flame retardants. However, it has beenfound through the study of the present invention that any flameretardant completely dissolves in a solvent if the concentration in thesolvent is approximately 5%. According to the present invention, theadditives can be separated and removed from the resin componentregardless of the type and the content of the additives in the resin byoptimizing the heating and kneading conditions. This is also one of theimportant features of the present invention.

Moreover, the means of heating and agitation herein referred may be anapparatus in which continuous kneading is possible such as an extruder,an injection machine, or a blow molding machine having a single screw ortwin screws, or may be an apparatus having the agitation function of abatch treatment type.

In addition, the solvent used for dissolving the additives according tothe present invention can be used repeatedly by a distillation operationor a filtering operation of the additives utilizing the temperaturedependence of the solubility of the additives, so that the amount of itsusage can be suppressed. Further, the additives recovered as a residueafter removing the solvent can be recovered without being diffused inair. Moreover, the volume of the recovered additives is very smallcompared with the weight of the total weight of the resin composition,so that it can be handled under special control.

Thus, according to the present invention, the treatment can be performedin the form in which the environment is given consideration such asappropriate treatment, recovery and recycling treatment of substanceshaving potential of environmental pollution, as well as a reduction ofthe amount of solvent used.

The treatment method of the present invention will now be described indetail.

The method of treating a thermoplastic resin composition containing anadditive according to the present invention comprises heating andagitating the thermoplastic resin composition containing the additivetogether with a solvent for dissolving at least part of the additive ata temperature ranging from the glass transition temperature of thethermoplastic resin to the boiling point of the solvent inclusive, andseparating and recovering the solvent in a liquid state in which atleast part of the additive is dissolved, so that at least part of theadditive is separated and removed from the thermoplastic resincomposition.

Although it is possible to dissolve at least part of the additive fromthe neighborhood of the resin surface area even in a temperaturecondition of the glass transition temperature or below of thethermoplastic resin composition, the rate of the removal may be smalland the condition may be insufficient in terms of efficiency. Thekneading and agitation treatment at the glass transition temperature orabove where heat distortion occurs allows removal of the additivecomponent present inside the resin, which is more desirable. Moreover,heating to a temperature of the boiling point or above of the solventfor dissolving at least part of the additive may cause thermaldegradation of the resin and may prevent the dissolution behavior of theadditive itself, resulting in reduction of the efficiency of theremoval. Therefore, the treatment in the temperature condition describedabove is desirable.

Moreover, there is a method of removing the solvent by a vacuum vent ofa kneader as a method of separating the solvent used for the reactionfrom a resin. However, this method recovers the solvent used for thereaction as steam, which is different from the form described in thepresent invention in which the solvent is recovered in a liquid state.In the case of the steam recovery, the additive cannot be separated andrecovered since only the solvent is finally recovered. Separation of thesolvent in a liquid state in which at least part of the additive isdissolved is an important point of the present invention.

The solubility parameter of the solvent for dissolving at least part ofthe additive contained in the thermoplastic resin composition accordingto the present invention is characterized by not smaller than thesolubility parameter value of the thermoplastic resincomponent+1((MPa)^(0.5) as the unit).

It is possible to dissolve the resin by using the solvent exhibiting asolubility parameter that is almost the same as that of the resin.However, by using the solvent having a solubility parameter exhibitingthe condition described in the present invention, the solubility of theresin itself can be suppressed and at the same time the solubility ofthe additive component can be improved, so that it becomes possible tocarry out the most suitable treatment.

Specifically, the solvent preferably includes one selected from thegroup consisting of glycol-based solvents, glycol ether-based solvents,lactic acid e lactate-based solvents, or alcohol-based solvents havingfive or more carbon atoms and mixtures thereof. These solvents typicallyhave relatively high boiling point, and exist in a liquid state evenduring heating and agitation, and heating and kneading treatment. Inaddition, they often have a high flash point, which is considered to bepreferable as the work environment will be safer.

The group of the above described compounds includes ethylene glycol,diethylene glycol, propylene glycol, dipropylene glycol, diethyleneglycol methyl ether, diethylene glycol ethyl ether, diethylene glycolpropyl ether, diethylene glycol butyl ether, propylene glycol methylether, propylene glycol ethyl ether, propylene glycol propyl ether,dipropylene glycol methyl ether, dipropylene glycol ethyl ether,dipropylene glycol propyl ether, dipropylene glycol butyl ether,triethylene glycol methyl ether, triethylene glycol ethyl ether,triethylene glycol propyl ether, triethylene glycol butyl ether,tripropylene glycol methyl ether, tripropylene glycol ethyl ether,tripropylene glycol propyl ether, tripropylene glycol butyl ether, ethyllactate, butyl lactate, 1-pentanol, 2-methyl-1-buthanol, iso-pentylalcohol, 1-hexanol, 2-methyl-1-pentanol, 4-methyl-2-pentanol,1-hepthanol, 2-ethyl-1-hexanol, 3,5,5-trimethyl-1-hexanol, and1-decanol.

As for the solvent to be used in the present invention, the higherconcentration of the above described compounds can enhance theinsolubility to styrenic polymers and enhance the solubility to theadditives. Therefore, the concentration of the above described compoundsis desirably as high as possible. Moreover, the concentration isdesirably such that the solvent is included as a main component and ispreferably at least 50% by weight or more of the weight of the totalsolvent.

Moreover, the additive contained in the thermoplastic resin compositionof the present invention may include an additive consisting of two ormore additive components. In this case, the removal and separation maybe performed with the same solvent and process to the greatest extentpracticable, but it is also possible to use the solvents that candissolve respective additives, although associated with the efficiencyof the removal and the complexity of the process. Further, the method ofremoving different types of additives may include separation and removalof specific additive components by mixing two or more differentsolvents. Alternatively, it is possible to take steps by repeating theabove described treatment method the time of the number of additivetypes; that is, after an additive 1 is removed and separated, anadditive 2 is separated and removed and further an additive 3 isseparated and removed. Therefore, a plurality of apparatuses may beprovided in such a way as removing the additive 1 in an apparatus 1 andthe additive 2 in an apparatus 2.

Moreover, the present invention proposes a method that can also treatthe case where the additives contained in the thermoplastic resincomposition include a bromine-based flame retardant and anantimony-based flame retardant auxiliary. The solvent that dissolves atleast part of the bromine-based flame retardant is selected from thegroup consisting of glycol-based solvents, glycol ether-based solvents,lactate-based solvents, or alcohol-based solvents having five or morecarbon atoms or mixtures thereof. Also, the solvent that dissolves atleast part of the antimony-based flame retardant auxiliary includes asolvent selected from the group consisting of ethylene glycol orpropylene glycol. It has been found this time that the use of therespective solvents allows separation and removal of at least part ofeach of the bromine-based flame retardant and the antimony-based flameretardant auxiliary from the thermoplastic resin composition.

Further, it has been found this time that when the bromine-based flameretardant and the antimony-based flame retardant auxiliary are containedin the thermoplastic resin composition, the efficiency of removalchanges depending on the order of the removal. Specifically, it ispossible to remove the bromine-based flame retardant and theantimony-based flame retardant auxiliary efficiently from thethermoplastic resin composition by separating and removing at least partof the bromine-based flame retardant from the thermoplastic resincomposition using the solvent selected from the group consisting ofglycol-based solvents, glycol ether-based solvents, lactate-basedsolvents, or alcohol-based solvents having five or more carbon atoms ormixtures thereof as the solvent for dissolving at least part of thebromine-based flame retardant, and then by separating and removing atleast part of the antimony-based flame retardant auxiliary from thethermoplastic resin composition using the solvent selected from ethyleneglycol or propylene glycol as the solvent for dissolving at least partof the antimony-based flame retardant auxiliary.

The apparatus for treating the thermoplastic resin compositioncontaining the additive according to the present invention has means ofcharging the solvent for dissolving at least part of the additive andthe thermoplastic resin composition containing the additive, means ofheating to a temperature ranging from the glass transition temperatureof the thermoplastic resin to the boiling point of the solventinclusive, means of agitating the thermoplastic resin compositioncontaining the additive and/or the solvent, and means of separating thesolvent in which at least part of the additive is dissolved to theoutside of the treatment apparatus in a liquid state.

As shown in FIG. 1, a specific apparatus is a reaction vessel 4 with anagitation function 5, having solvent and resin inlets 1, 1′, an outlet 2for separating the solvent in which at least part of an additive isdissolved and a heater 3.

The means of charging the solvent and the thermoplastic resincomposition may include an inlet that shares the charge of the bothmaterials, or may include different inlets for respective materials.Alternatively, the solvent and the resin composition are preliminarilymixed and kneaded before the means of charging. Moreover, although theoutlet for separating the solvent in which at least part of the additiveis dissolved needs to be provided, the remained resin composition can betaken out in various ways. It may be taken out from the resin inletwithout providing a specific outlet, or a specific outlet for the resinmay be provided. It is desirable to obtain a desired resin compositionby single treatment for heating and agitation and separation of asolvent, but two or more treatments may be performed in terms of removalrate or operability without any problem.

In addition, an apparatus of treating the thermoplastic resincomposition containing the additive according to the present inventionincorporates a single or a plurality of screws connected with a centeraxis in a cylinder holding a heating mechanism. A drive mechanism isprovided at the base end of the screw axis to rotate it, and an inletfor the thermoplastic resin composition containing the additive and aninlet for the solvent for dissolving at least part of the additive areprovided in the neighborhood of the base end of the screw axis. Thescrew axis is arranged such that the rotation thereof transfers thethermoplastic resin composition containing the additive and the solventfrom the base end side toward the leading end side while pressuring,heating and kneading them. At the location closer to the leading endside than the inlet, there is provided an outlet for discharging thesolvent in a liquid state in which at least part of the additive isdissolved. At the leading end, there is provided an extrusion sectionfor extruding the kneaded and molten thermoplastic resin compositionfrom which at least part of the additive is separated and removed.

As shown in FIG. 2, a specific apparatus capable of practicing thepresent invention comprises a typical extruder 11 with a solvent inlet17 and a solvent outlet 18, that is provided with a hopper 12 that is aresin inlet, a screw 13 to transfer the charged resin toward a leadingend side while kneading, the screw 13 being held in a cylinder 15 havinga heater 14, a motor 16 to rotate the screw axis placed at the base endof the screw 13, and a resin outlet 19.

The extruder 11 includes a single extruder and a twin extruder, but inthis case the twin extruder having high kneading effect is particularlysuitable. At this time, a filter-type separator can be provided in thevicinity of the solvent outlet to separate a low viscosity solvent froma resin composition. Alternatively, the separation can also be enhancedby adjusting the pitch and shape of the screw. Any procedure may be usedto separate a solvent from a resin. In addition, a vent may be providedas a deaeration port for the purpose of removing a high boiling pointsolvent used for kneading at a location between the solvent outlet andthe resin outlet. Further, the vent can also be recovered as a steamcomponent using the means such as a vacuum pump.

A further preferred apparatus of treating a thermoplastic resincomposition containing an additive according to the present invention isthe one having an inlet for the solvent for dissolving at least part ofthe additive and an outlet for discharging the solvent in a liquid statein which at least part of the additive is dissolved, in which the inletand the outlet constitutes a pair in this order from the base end towardthe leading end, and at least two or more of the pairs are disposedrepeatedly. Although one inlet 17 and one outlet 18 are provided in FIG.2, the inlet and the outlet may be provided in plural numbers in termsof the removing rate of the additive to be removed. The important pointis that the inlet and the outlet are preferably disposed repeatedly inthis order from the base end side toward the leading end side.

In addition, in the apparatus of treating the thermoplastic resincomposition containing the additive according to the present invention,the outlet for discharging the solvent in a liquid state in which atleast part of the additive is dissolved is preferably disposed at alower side than the screw axis. Such a form can reduce the migration ofthe solvent to the leading end side compared with discharging thesolvent in a liquid form from an upper side. Therefore, it is possibleto reduce the residual solvent in the resin and decrease the venttreatment or the like that follows.

As described above, it is possible to combine the apparatusesillustrated in FIGS. 1 and 2 in plural numbers, providing the treatmentapparatus that can exert excellent capability. For example, in the casewhere a plurality of additives is included, an additive component 1 isremoved by a batch treatment by agitation, and then an additivecomponent 2 may be removed by a continuous treatment by kneading.Moreover, even in the case of only one additive, the use of differentsolvents allows maximization of the removing rate.

The present invention will now be described in detail with reference toexamples.

EXAMPLE 1

In the present example, a thermoplastic resin composition consisting ofa bromine-based flame retardant having a tetrabromobisphenol A-basedstructure as an additive component and polystyrene (a weight averagemolecular weight of the resin of 105,000 and a solubility parameter ofthe polystyrene of 18.6) as a resin component was prepared, and theflame retardant component contained in the resin composition was to beseparated. At this time, the amount of the flame retardant was adjustedsuch that it was contained in 15 parts by weight relative to the resincomposition.

A schematic view of an apparatus for use in the present example is shownin FIG. 3. This apparatus is a reaction vessel 4 with an agitationfunction 5, having solvent and resin inlets 1, 1′, an outlet 2 forseparating the solvent in which at least part of the flame retardant isdissolved and a heater 3.

The resin composition was first roughly ground to blocks of about 5 mmsquare and fed to the apparatus of FIG. 3 together with dipropyleneglycol 7 (a solubility parameter of 20.5), followed by agitation atabout 180° C. for two hours. The liquid in which the flame retardant wasdissolved was then recovered from the outlet. After the apparatus wassufficiently stood to cool, the resin component 6 was recovered from theinlet.

The remained amount of the flame retardant in the obtained resin wasdetermined by GPC, and it was found that the flame retardant was removeddown to 5% relative to 100% of the initial weight. In addition, theweight average molecular weights were determined for the polystyrenesbefore and after the treatment, and no significant difference was foundin the change of the molecular weight. Therefore, the recoveredpolystyrene was found to be reusable as a raw material. The residualsolvent in the resin was about 8%. It was found that 98% of the initialweight of the original solvent could be recycled by solidifying andseparating the flame retardant component by distillation.

EXAMPLE 2

In the present example, a thermoplastic resin composition consisting ofa bromine-based flame retardant of decabromodiphenyl ether as anadditive component and polystyrene (a weight average molecular weight ofthe resin of 100,000 and a solubility parameter of the polystyrene of18.6) as a resin component was prepared, and the flame retardantcomponent contained in the resin composition was to be separated. Atthis time, the amount of the flame retardant was adjusted such that itwas contained in 12 parts by weight relative to the resin composition.

A schematic view of an apparatus for use in the present example is shownin FIG. 4. This apparatus comprises a twin-screw extruder 11 with asolvent inlet 17 and a solvent outlet 18, that is provided with a hopper12 that is an inlet of a resin, a screw 13 to transfer the charged resintoward a leading end side while kneading, the screw 13 being held in acylinder 15 having a heater 14, a motor 16 to rotate the screw axisplaced at the base end of the screw 13, a resin outlet 19.

The heater 14 for the cylinder 15 was first set at 180° C. The resincomposition that was roughly ground to 5 mm square was supplied from thehopper 12 and dipropylene glycol (a solubility parameter of 20.5) wasadded from the solvent inlet 17, and they were subjected to heating andkneading treatment. At this time, the segment of the screw 13 wasadjusted such that the solvent in which the flame retardant componentwas dissolved was discharged from the outlet 18.

The solvent was charged in an amount of 5.0 relative to the amount ofcharged resin of 1.0, and the amount of recovered solvent was 4.9 aftercalculating the increase for the separated flame retardant and thedecrease for the solvent that remained in the resin. After that, avacuum pump 21 was provided to a vent 20 through a solvent trap 22; theresin was discharged from a resin outlet 19; and resin pellets 25 wereobtained through a cooling bath 23 and a cutter 24.

The remained amount of the flame retardant in the obtained resin wasdetermined by GPC, and it was found that the flame retardant was removeddown to 5% relative to 100% of the initial weight. In addition, theweight average molecular weights were determined for the polystyrenesbefore and after the treatment, and no significant difference was foundin the change of the molecular weight. Therefore, the recoveredpolystyrene was found to be reusable as a raw material. The residualsolvent in the resin was about 2%. It was found that 98% of the initialweight of the original solvent could be recycled by solidifying andseparating the flame retardant component by distillation.

EXAMPLE 3

In the present example, the same thermoplastic resin composition as usedin Example 2 was prepared and the removal treatment of a flame retardantwas performed using the apparatus as shown in FIG. 5. The differencebetween FIGS. 4 and 5 is that in addition to a solvent inlet 17 and asolvent outlet 18, another pair of solvent inlet 27 and solvent outlet28 was provided at locations closer to the leading end.

The heater 14 for the cylinder 15 was first set at 170° C. The resincomposition that was roughly ground to 5 mm square was supplied from thehopper 12 and propylene glycol (a solubility parameter of 25.8) wasadded from the first solvent inlet 17, and they were subjected toheating and kneading treatment. At this time, the segment of the screw13 was adjusted such that the solvent in which the flame retardantcomponent was dissolved was discharged from the first outlet 18. Thesame operation was performed for the second solvent inlet 27 and thesecond solvent outlet 28. At this time, both of the first and the secondsolvent were charged in an amount of 5.0 relative to the amount ofcharged resin of 1.0. The amounts of recovered solvent were 4.9 and 4.8for the first and the second, respectively. After that, a vacuum pump 21was provided to a vent 20 through a solvent trap 22; the resin wasdischarged from a resin outlet 19; and resin pellets 25 were obtainedthrough a cooling bath 23 and a cutter 24.

The remained amount of the flame retardant in the obtained resin wasdetermined by GPC, and it was found that the flame retardant was removeddown to 1.8% relative to 100% of the initial weight. The amount of thecharged solvent was increased compared with Example 2, and it was foundthat the flame retardant contained in the thermoplastic resin wasremoved in more quantities. In addition, the weight average molecularweights were determined for the polystyrenes before and after thetreatment, and no significant difference was found in the change of themolecular weight. Therefore, the recovered polystyrene was found to bereusable as a raw material. The residual solvent in the resin was about3%. When the treatment with the vacuum pump at the vent was notperformed, it was about 8%. Thus, the effect of adding the vent wasconfirmed. It was found that 98% of the initial weight of the originalsolvent could be recycled by solidifying and separating the flameretardant component by distillation.

EXAMPLE 4

In the present example, the same thermoplastic resin composition as usedin Example 2 was prepared and the removal treatment of a flame retardantwas performed using the apparatus as shown in FIG. 6. The differencebetween FIGS. 5 and 6 is that two solvent outlets 18 and 28 wereprovided at locations lower than the kneader.

The heater 14 for the cylinder 15 was first set at 180° C. The resincomposition that was roughly ground to 5 mm square was supplied from thehopper 12 and dipropylene glycol (a solubility parameter of 20.5) wasadded from the first solvent inlet 17, and they were subjected toheating and kneading treatment. At this time, the segment of the screw13 was adjusted such that the solvent in which the flame retardantcomponent was dissolved was discharged from the first outlet 18. Thesame operation was performed for the second solvent inlet 27 and thesecond solvent outlet 28. At this time, both of the first and the secondsolvent were charged in an amount of 5.0 relative to the amount ofcharged resin of 1.0. The amounts of recovered solvent were 4.9 and 5.0for the first and the second, respectively. After that, a vacuum pump 21was provided to a vent 20 through a solvent trap 22; the resin wasdischarged from a resin outlet 19; and resin pellets 25 were obtainedthrough a cooling bath 23 and a cutter 24.

The remained amount of the flame retardant in the obtained resin wasdetermined by GPC, and it was found that the flame retardant was removeddown to 1.2% relative to 100% of the initial weight. In addition, theweight average molecular weights were determined for the polystyrenesbefore and after the treatment, and no significant difference was foundin the change of the molecular weight. Therefore, the recoveredpolystyrene was found to be reusable as a raw material. The residualsolvent in the resin was about 1%, which was found to be less than thatfor Example 3. It was found that 98% of the initial weight of theoriginal solvent could be recycled by solidifying and separating theflame retardant component by distillation.

EXAMPLE 5

In the present example, a thermoplastic resin composition consisting of15 parts by weight of a bromine-based flame retardant of atetrabromobisphenol A-based epoxy oligomer-type and 3 parts by weight ofantimony trioxide as additive components and high-impact polystyrene (aweight average molecular weight of the resin of 120,000 and a solubilityparameter of 17.6 to 18.6) as a resin component was prepared, and theflame retardant component and the flame retardant auxiliary contained inthe resin composition was to be separated. The apparatus shown in FIG. 6was used for the separation treatment.

The heater 14 for the cylinder 15 was first set at 180° C. The resincomposition that was roughly ground to 5 mm square was supplied from thehopper 12 and dipropylene glycol (a solubility parameter of 20.5) wasadded in an amount five times the weight of the charged resin from thefirst solvent inlet 17, and they were subjected to heating and kneadingtreatment. At this time, the segment of the screw 13 was adjusted suchthat the solvent in which the flame retardant components were dissolvedwas discharged from the first outlet 18. Then, ethylene glycol (asolubility parameter of 29.9) was added in an amount three times theweight of the charged resin from the second solvent inlet 27, and theywere subjected to the same heating and kneading treatment before thesolvent was discharged from the second outlet 28. The amounts ofrecovered solvent were 4.9 and 3.0 for the first and the second,respectively. After that, a vacuum pump 21 was provided to a vent 20through a solvent trap 22; the resin was discharged from a resin outlet19; and resin pellets 25 were obtained through a cooling bath 23 and acutter 24.

The remained amount of the flame retardant in the obtained resin wasdetermined by GPC, and it was found that the flame retardant was removeddown to 1.8% relative to 100% of the initial weight. Also, by afluorescent X-ray analysis, it was confirmed that the concentration ofantimony in the resin decreased to about 20% of the initialconcentration. In addition, the weight average molecular weights weredetermined for the polystyrenes before and after the treatment, and nosignificant difference was found in the change of the molecular weight.Therefore, the recovered polystyrene was found to be reusable as a rawmaterial. The residual solvent in the resin was about 0.8%. It was foundthat 98% of the initial weight of the used solvents could be recycled bydistillation operations for each of the solvents.

EXAMPLE 6

In the present invention, the study was performed using the samethermoplastic resin composition as used in Example 5. The treatmentapparatus that was used is also the same.

The heater 14 for the cylinder 15 was first set at 180° C. The resincomposition that was roughly ground to 5 mm square was supplied from thehopper 12 and ethylene glycol (a solubility parameter of 29.9) was addedin an amount five times the weight of the charged resin from the firstsolvent inlet 17, and they were subjected to heating and kneadingtreatment. At this time, the segment of the screw 13 was adjusted suchthat the solvent in which the flame retardant components were dissolvedwas discharged from the first outlet 18. Then, ethylene glycol (asolubility parameter of 29.9) was added in an amount three times theweight of the charged resin also from the second solvent inlet 27, andthey were subjected to the same heating and kneading treatment beforethe solvent was discharged from the second outlet 28. The amounts ofrecovered solvent were 4.9 and 3.0 for the first and the second,respectively. After that, a vacuum pump 21 was provided to a vent 20through a solvent trap 22; the resin was discharged from a resin outlet19; and resin pellets 25 were obtained through a cooling bath 23 and acutter 24.

The remained amount of the flame retardant in the obtained resin wasdetermined by GPC, and it was found that the flame retardant remained by20% relative to 100% of the initial weight. Also, by a fluorescent X-rayanalysis, it was confirmed that the concentration of antimony in theresin decreased to about 50% of the initial concentration. The removalrate was lower than Example 5. It was able to be confirmed that the samesolvent was usable for removing both of the additives. However, it canbe judged that each of the additives is preferably removed withdifferent solvents as in Example 5 in terms of the removal rate. Inaddition, the weight average molecular weights were determined for thepolystyrenes before and after the treatment, and no significantdifference was found in the change of the molecular weight. Therefore,the recovered polystyrene was found to be reusable as a raw material.The residual solvent in the resin was about 0.8%. It was found that 98%of the initial weight of the used solvent could be recycled bydistillation.

EXAMPLE 7

In the present invention, the study was performed using the samethermoplastic resin composition as used in Example 5. The treatmentapparatuses that were used were the one shown in FIG. 3 for treating thebromine-based flame retardant and the one shown in FIG. 4 for treatingthe antimony-based flame retardant auxiliary.

The resin composition was first roughly ground to blocks of about 5 mmsquare and was fed to the apparatus of FIG. 3 together with dipropyleneglycol 7 (a solubility parameter of 20.5), followed by agitation at 180°C. for two hours. The liquid in which the flame retardant was dissolvedwas then recovered from the outlet. After the apparatus was sufficientlystood to cool, the resin component 6 was recovered from the inlet.

Then, the treatment was continued using the apparatus shown in FIG. 4.Specifically, the heater 14 for the cylinder 15 was set at 180° C. Therecovered thermoplastic resin composition from which at least part ofthe bromine-based flame retardant was removed was supplied from thehopper 12 and ethylene glycol (a solubility parameter of 29.9) was addedin an amount three times the weight of the charged resin from thesolvent inlet 17, and they were subjected to heating and kneadingtreatment. At this time, the segment of the screw 13 was adjusted suchthat the solvent in which the flame retardant components were dissolvedwas to be discharged from the outlet 18. The amount of the solventrecovered was 3.0. After that, a vacuum pump 21 was provided to a vent20 through a solvent trap 22; the resin was discharged from a resinoutlet 19; and resin pellets 25 were obtained through a cooling bath 23and a cutter 24.

The remained amount of the flame retardant in the obtained resin wasdetermined by GPC, and it was found that the flame retardant was removeddown to 5% relative to 100% of the initial weight. Also, by afluorescent X-ray analysis, it was confirmed that the concentration ofantimony in the resin decreased to about 10% of the initialconcentration. In addition, the weight average molecular weights weredetermined for the polystyrenes before and after the treatment, and nosignificant difference was found in the change of the molecular weight.Therefore, the recovered polystyrene was found to be reusable as a rawmaterial. The residual solvent in the resin was about 0.8%. It was foundthat 98% of the initial weight of the used solvents could be recycled bydistillation operations for each of the solvents.

EXAMPLE 8

In the present example, a thermoplastic resin composition consisting of0.1 part by weight of a phenol-based antioxidant and 0.3 part by weightof a sulfur-based antioxidant as additive components and polypropylene(a weight average molecular weight of the resin in terms of polystyreneof 100,000 and a solubility parameter of 18.8) as a resin component wasprepared, and the antioxidant components contained in the resincomposition were to be separated. The apparatus that was used is thesame as shown in FIG. 3.

The resin composition was first roughly ground to blocks of about 5 mmsquare and was fed to the apparatus of FIG. 3 together with2-methyl-1-pentanol (a solubility parameter of 21.3), followed byagitation at about 125° C. for two hours. The liquid in which theadditives were dissolved was then recovered from the outlet. After theapparatus was sufficiently stood to cool, the resin component wasrecovered from the inlet.

The remained amount of the additives in the obtained resin wasdetermined by GPC by comparing with initial peaks, and it was found thatthe additives were removed down to 3% relative to 100% of the initialweight. In addition, the weight average molecular weights weredetermined for the resins before and after the treatment, and nosignificant difference was found in the change of the molecular weight.Therefore, the recovered resin was found to be reusable as a rawmaterial. The residual solvent in the resin was about 3%.

EXAMPLE 9

In the present invention, the study was performed using the same resincomposition as used in Example 6.

The resin composition was first roughly ground to blocks of about 5 mmsquare and was fed to the apparatus of FIG. 3 together with ethyllactate (a solubility parameter of 20.5), followed by agitation at about170° C. for two hours. The liquid in which the additives were dissolvedwas then recovered from the outlet. After the apparatus was sufficientlystood to cool, the resin component was recovered from the inlet.

The remained amount of the additives in the obtained resin wasdetermined by GPC by comparing with initial peaks, and it was found thatthe additives were removed down to 2% relative to 100% of the initialweight. In addition, the weight average molecular weights weredetermined for the resins before and after the treatment, and nosignificant difference was found in the change of the molecular weight.Therefore, the recovered resin was found to be reusable as a rawmaterial. The residual solvent in the resin was about 5%.

As described above, the use of the treatment method and the treatmentapparatus according to the present invention allows separation andremoval of only the additives that become unnecessary from thethermoplastic resin composition used in waste home electric applianceswhich will be discarded in great quantities in future and will become aproblem. In addition, the recycle of the resin achieves reduction of theamount of wastes, and also the solvent used for the regeneration can bereused. Thus, these will be of some help to the solution ofenvironmental issues that is now needed.

1. A method of treating a thermoplastic resin composition containing astyrenic thermoplastic resin, a bromine-based flame retardant and anantimony-based flame retardant auxiliary, characterized by comprising: astep (a) of heating and agitating said thermoplastic resin compositiontogether with a first solvent containing at least one selected fromglycol-based solvents, glycol ether-based solvents, and lactate-basedsolvents at a temperature ranging from a glass transition temperature ofsaid thermoplastic resin to a boiling point of said first solventinclusive; and separating and recovering said first solvent in a liquidstate in which at least part of said bromine-based flame retardant isdissolved from said thermoplastic resin composition, so that at leastpart of said bromine-based flame retardant is separated and removed fromsaid thermoplastic resin composition and; a step (b) of heating andagitating said thermoplastic resin composition together with a secondsolvent containing at least one selected from ethylene glycol andpropylene glycol at a temperature ranging from a glass transitiontemperature of said thermoplastic resin to a boiling point of saidsecond solvent inclusive; and separating and recovering said secondsolvent in a liquid state in which at least part of said antimony-basedflame retardant auxiliary is dissolved from said thermoplastic resincomposition, so that at least part of said antimony-based flameretardant auxiliary is separated and removed from said thermoplasticresin composition, wherein said step (b) is performed after said step(a) or said step (a) is performed after said step (b).
 2. The method oftreating a thermoplastic resin composition according to claim 1,characterized in that said styrenic thermoplastic resin contains any oneof polystyrene, poly-α-methyl styrene, poly-(styrene-butadiene),poly-(styrene-acrylonitrile), poly-(styrene-butadiene-acrylonitrile),poly-(styrene-maleic anhydride), and impact-resistant high-impactpolystyrene.
 3. The method of treating a thermoplastic resin compositionaccording to claim 1, wherein step (b) is performed after said step (a).